The nutritional interactions of vitamin B12 deficiency and methionine with folic acid will be studied in the rat. Rats will be fed diets deficient in vitamin B12 and methionine or exposed to nitrous oxide. Folate coenzyme levels will be measured by HPLC and the activities of methionine synthetase (MS) and methylenetetrahydrofolate reductase (MTR) estimated in bone marrow, brain, and small intestine. Graduated amounts of methionine will be administered to the rats prior to these measurments to determine its effects on folate metabolism. Others have shown in liver, vitamin B12 deficiency resulted in trapping of folates as 5-methyltetrahydrofolate. Methionine, via S-adenosylmethionine, reversed this trapping of folates. Bone marrow cells from rats fed vitamin B12 deficient diets showed no trapping of folates and no decrease in MS activity. High levels of methionine resulted in trapping of folates as the 5-methyly derivative. The proposed studies are designed to investigate the reasons for this difference in bone marrow cells and to study vitamin B12-folate interactions in the other susceptible organs - brain and small intestine. The implications of oral contraceptive use in regards to folic acid nutriture is another goal of this application. Oral contraceptive induced localized folate deficiency has been implicated in megaloblastic changes in cervical epithelial cels and in the progression of cervical dysplasia. Folic acid supplementation improved these problems. In female rats, oral contraceptives increased the level of 5-methyltetrahydrofolate. This might explain the megaloblastic changes seen in oral contraceptive users. Female rats will be fed diets limiting in methionine. oral contraceptives will be given daily for several weeks. At various times, folate coenzyme levels will be measured by HPLC in liver and uterus. The effects of oral contraceptives on MS and MTR activities and on folate binding proteins also will be determined in these organs. Proteins are present in plasma which bind folates. Much work has been done on these proteins but their function remains unknwon. The endogenous ligand bound to folate binding protein will be identified by chromatographic separation of the binding proteins in plasma and HPLC of the dissociated ligand. The protein will be purified by standard and affinity chromatographic techniques. The purifed protein will be labeled with radioactive folate and its ability to deliver folate to tissues will be studied.